1. Field of the Invention
The present invention relates to an X-ray imaging technique.
2. Description of the Related Art
Conventionally, an X-ray imaging apparatus used in a hospital or the like uses a cassette. After an exposed cassette is developed, the developed film is interpreted by using an observation device called a film viewer. With the recent advances in computer technology, it is possible to perform a series of operations from imaging to interpretation with digital images. Use of a portable FPD (Flat Panel Detector) instead of a conventional cassette can implement digital image processing. For example, the above conventional technique is disclosed in Japanese Patent Laid-Open No. 3-251231.
When general X-ray imaging with a cassette is to be performed, the cassette is set at a predetermined position. A subject is then placed on the cassette, and X-ray imaging is performed. In this case, it is necessary to perform positioning such that the central axis of X-ray irradiation from an X-ray tube becomes perpendicular to the light-receiving surface of the cassette.
In the method using a cassette, however, an angle detection result cannot be used for X-ray control during imaging.